Photovoltaic (PV) or solar cells are material junction devices which convert sunlight into direct current (DC) electrical power. When exposed to sunlight, the electric field of solar cell p-n junctions separates pairs of free electrons and holes, thus generating a photo-voltage. A circuit from n-side to p-side allows the flow of electrons when the solar cell is connected to an electrical load, while the area and other parameters of the PV cell junction device determine the available current. Electrical power is the product of the voltage times the current generated as the electrons and holes recombine.
Thin-film solar devices typically consist of multiple thin layers of material deposited on sheet glass. These glass panels are typically subdivided into a large number (between 100 and 200) of individual solar cells by scribing processes that also define the electrical interconnects for adjacent cells, which are electrically connected in series to produce power with a current. Laser scribing enables high-volume production of next-generation thin-film devices, and laser scribing ouTperforms mechanical scribing methods in quality, speed, and reliability.
The laser-material interaction involves complex processes of heating, melting, vaporization, ejection of atoms, ions and molecules, shock waves, plasma initiation and plasma expansion. The resulting crater and laser-induced plasma are dependent on the laser beam parameters (e.g., duration, energy, and wavelength), the solid target properties, and the surrounding environment's conditions.
The laser scribes are desirably controlled to a specific depth to control the properties of the individual cells and resulting module formed. However, due at least in part to the different material composition of each thin film, the energy (e.g., the intensity of the laser and/or the time applied) required to scribe each individual thin film layer in the film stack can vary. As such, accurately controlling the depth of the laser scribe can be a calculation based on the sum of the energy required to scribe each layer. This calculation can lead to variations in the depth of the laser scribe formed through the many layers. Such variations in depth can, in turn, lead to variations in performance of the resulting PV module.
As such, a need exists for more precisely laser scribing multiple thin films on a glass supersubstrate, especially cadmium telluride based thin film photovoltaic devices.